A. Field of the Invention
The present invention relates to an improved disc drive apparatus. More specifically, the invention relates to a technique of preventing flotation of a disc-shaped recording medium in a disk drive apparatus.
B. Related Fields
In disc drive apparatuses, for example, replaceable disc drive apparatuses such as a CD-ROM drive, a sealed structure is provided above the disc-shaped recording medium as a countermeasure against the intrusion of dust thereinto. The portion below the disc-shaped recording medium is provided with a head for information reading, a spindle motor for rotating the disc-shaped recording medium, and other components.
When a disc-shaped recording medium is rotated at high speed, the air under the disc-shaped recording medium can circulate in such a manner as to flow to the outside of the disc-shaped recording medium and pass by the spindle motor. However, the air over the disc-shaped recording medium cannot circulate because even if it flows to the outside of the disc-shaped recording medium it cannot go further due to the relatively small size (height) of the space over the disc-shaped recording medium. Therefore, the air pressure in the sealed space over the disc-shaped recording medium becomes lower than that in the portion under the disc-shaped recording medium. As a result, the disc-shaped recording medium is disadvantageously sucked up (floated up) because of this air pressure difference.
To reduce cost, the spindle motor has used a sintered oil-retaining metal as a bearing. In addition, the spindle motor causes the rotor to be pressed downwardly only by an attraction force that is generated by utilizing a deviation between the magnetic center of a rotor magnet and that of the iron core of each stator coil.
In the disc drive apparatus having such an arrangement, with an increase in speed, it has become difficult to prevent flotation of the disc-shaped recording medium only by using the attractive force of the rotor magnet. As a consequence thereof, read errors occur more frequently.
Previous methods for preventing flotation of the disc-shaped recording medium include the use of another magnet (in addition to the rotor magnet) that is dedicated to retaining the rotor there below and the use of a ball bearing instead of a sintered oil-retaining metal bearing. However, in requiring an additional component, these methods have been found to be costly.
It is an object of this invention to provide a disk drive apparatus which avoids the above-noted deficiencies of the prior art.
It is also an object of this invention to provide a disk drive apparatus which reduces read errors.
It is a further object of this invention to provide a disk drive apparatus which prevents disc-shaped recording medium from floating at high speed which does not require additional components, such as another magnet (in addition to the rotor magnet) or the use of a ball bearing.
It is a further object of this invention to provide a disc drive apparatus which prevents flotation of a disc-shaped recording medium without causing cost increase.
To solve the above problems, in a disc drive apparatus according to the invention, a top plate includes air passages that extend in radial directions of a disc-shaped recording medium.
Therefore, in the disc drive apparatus according to the invention, air that has passed from a central portion to a peripheral portion due to rotation of the disc-shaped recording medium returns to the central portion via the air passages of the top plate so that reduction in air pressure is prevented over the disc-shaped recording medium. As a result, flotation of the disc-shaped recording medium can be prevented without the need for using an expensive additional component.